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Abstract:

A screen printing apparatus is described. The apparatus has a plurality
of radial arms each having a printing head associated therewith. A target
area is in alignment with at least one of the printing heads wherein a
design is applied to a target article at the target area by the printing
head. A means for providing relative movement between the target area and
the printing head provides multiple passes between a squeegee associated
with the printing head and the target area. A means for providing a
pressure between the squeegee and the target area is regulated such that
a first pressure between the squeegee and the target area on a first
stroke is not equal to a second pressure between the squeegee and the
target area on a subsequent second stroke.

Claims:

1. A method of screen printing a fabric target using an automated screen
printing apparatus comprising at least one printing head having a flood
bar for delivering a quantity of fluid to a screen and a squeegee for
applying a force by which at least a portion of the fluid passes through
the screen to the fabric target, the method comprising the steps of:
providing a first relative movement between the squeegee and the screen;
providing engagement between the squeegee and the screen with a first
force between the squeegee and the screen during the first providing
relative movement step; providing a second relative movement between the
squeegee and the screen; and providing engagement between the squeegee
and the screen with a second force between the squeegee and the screen
during the second providing relative movement step wherein the first
force is not equal to the second force.

2. The method of claim 2 wherein the screen is laden with a printing
fluid.

3. A method of screen printing a fabric target comprising the steps of:
providing a printing head including screen having a pattern thereon, a
flood bar for delivering a quantity of an ink to the screen and a
squeegee for applying a force by which at least a portion of the ink
passes through the screen to the fabric target; providing an
electro-mechanical means for providing movement to the flood bar and the
squeegee across the screen; providing a source of pressure for applying a
force to the squeegee against the screen; providing a means for automated
regulation of the source of pressure wherein the force applied to the
squeegee may be automatically varied from a first magnitude of force
applied on a first stroke of the squeegee across the screen to a second
magnitude of force applied on a second stroke of the squeegee across the
screen wherein the second magnitude of force is less than the first
magnitude of force.

4. A turret-style printing apparatus comprising: a plurality of radial
arms each having a printing head associated therewith; a target area in
alignment with at least one printing head wherein a design is applied to
a target article at the target area by the at least one printing head;
means for providing relative movement between the target area and the at
least one printing head wherein the means for providing relative movement
provides multiple passes between a squeegee and the target area; means
for providing a pressure between the squeegee and the target area; and
means for automatically regulating the pressure between the squeegee and
the target area wherein a first pressure between the squeegee and the
target area on a first stroke is not equal to a second pressure between
the squeegee and the target area on a subsequent second stroke.

5. An automated screen printing apparatus comprising: a multi-stroke
printing head having a squeegee operatively engaged with a source of
pressure transferring a force to the squeegee; and a means for
controlling the source of pressure wherein the means for controlling the
source of pressure selectively varies the force applied to the squeegee
from a first applied force applied during a first stroke to a second
applied force applied during a subsequent stroke.

6. The automated screen printing apparatus of claim 5 wherein the first
applied force is not equal to the second applied force.

7. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure selectively varies the force
applied to the squeegee from the first applied force applied during the
first stroke to a plurality of applied forces applied during a plurality
of corresponding subsequent strokes.

8. The automated screen printing apparatus of claim 7 wherein a digital
voltage regulator provides the means for controlling the source of
pressure.

9. The automated screen printing apparatus of claim 7 wherein an analog
signal provides the means for controlling the source of pressure.

11. The automated screen printing apparatus of claim 6 further
comprising: a control panel for selectively means for controlling the
source of pressure.

12. The automated screen printing apparatus of claim 11 further
comprising: a pressure display on the control panel.

13. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure is adjustable via a display panel
spaced from the printing head.

14. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure is adjustable at the multi-stroke
printing head.

15. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure is adjustable at a plurality of
locations positioned about the apparatus.

16. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure is adjustable at a remote
location.

17. The automated screen printing apparatus of claim 6 wherein the means
for controlling the source of pressure may be disabled wherein the first
applied force applied during a first stroke and the second applied force
applied during a subsequent stroke are equal in magnitude.

18. The automated screen printing apparatus of claim 6 wherein at least
one piston transfers the first and second forces to the squeegee.

19. A printing head for an automated screen printing machine, the
printing head comprising: a squeegee operatively engaged by a source of
pressure; and a means for varying a force applied by the source of
pressure to the squeegee.

20. The printing head of claim 19 wherein the means for varying a force
applied by the source of pressure to the squeegee selectively varies the
force applied to the squeegee from a first applied force applied during a
first stroke to a second applied force applied during a subsequent
stroke.

21. The printing head of claim 20 wherein the first applied force is not
equal to the second applied force.

22. The printing head of claim 21 further comprising: a flood bar
adjacent the squeegee operatively engaged by a source of pressure.

23. A method of screen printing a fabric target using an automated screen
printing apparatus comprising at least one printing head having a flood
bar for delivering a quantity of fluid to a screen and a squeegee for
applying a force by which at least a portion of the fluid passes through
the screen to the fabric target, the method comprising the steps of:
providing a first relative movement between the squeegee and the screen;
providing engagement between the squeegee and the screen with a first
force between the squeegee and the screen during the first providing
relative movement step; providing a second relative movement between the
squeegee and the screen; and providing engagement between the squeegee
and the screen with a second force between the squeegee and the screen
during the second providing relative movement step wherein the first
force is not equal to the second force.

24. The method of claim 23 wherein the screen is laden with a printing
fluid.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application
No. 61/030,804, filed on Feb. 22, 2008 and is hereby incorporated by
reference as if fully set forth herein

TECHNICAL FIELD

[0002] The present invention relates generally to printing machines and,
more particularly, to a multi-stroke printing head with variable
pressure.

BACKGROUND OF THE INVENTION

[0003] Typically, in a print stroke of a screen printing machine, a
squeegee will pass over the screen once, pushing the ink through the mesh
openings in the screen. Some systems will have a feature permitting a
second print stroke, or a second pass over the screen. It is widely
believed that this will produce a thicker and smoother image on the
textile being printed upon. The second print stroke, if selected, will be
at the same pressure as the first stroke. It is well known that squeegee
pressure, which translates to the pressure or force the squeegee places
upon the screen during the print stroke, affects the amount of ink pushed
through the gaps or openings on the screen and onto the textile being
printed upon. Accordingly, many falsely believe the more ink deposited
upon the textile, the better the results. This is wrong in many
instances. Merely adding pressure to the squeegee and/or adding print
strokes does not always improve the quality of the finished product.

[0004] Rather, it has been found that for several reasons, customizing the
pressure of the strokes and the adding of strokes improve the quality of
the image. For example, there are many factors contributing to the image
created on the textile. As a starter, these include the ink employed and
the textile printed upon. Different inks behave differently and different
textiles act differently.

[0005] Inks include Plastisol (with and without additives, such as
expanding inks), water based inks, PVC/Phalate Free, discharge inks
(which remove die), foil, glitter/shimmer, metallic, caviar beads,
glosses, nylobond, mirrored silver and other solvent based inks. Textiles
include natural and artificial fibers from animals (e.g., wool and silk),
plants (e.g., cotton, flax, jute, hemp, modal, pina and ramie), minerals
(e.g., glass fibers) and synthetics (e.g., polyester, aramid, acrylic,
nylon, spandex/polyurethane, olefin, ingeo and lurex). Each combination
of ink and textile will demonstrate different properties, such as those
associated with wicking, holding, hand, penetration and appearance.
Accordingly, a one-size-fits-all approach does not necessarily produce
the best results. Specifically, it has been found the appearance of an
image will change on a textile with multiple printings at the same or
different pressures. For example, performing three print strokes while
incrementally increasing the squeegee's pressure on the screen (and hence
the textile) will produce different results than performing three print
strokes while incrementally decreasing the squeegee's pressure on the
screen. With one combination of ink and textiles the multiple strokes
increasing may be better and with another combination of ink and textiles
the multiple strokes decreasing may be better.

[0006] In summary, permitting one to selectively increase the number of
print strokes by a squeegee and vary the pressure applied by the squeegee
gives one additional options and important tools towards improving the
final printed product.

[0007] Applicants of the present invention have also recognized the final
image on the textile can often be greatly improved if the textile is
"kissed" by the screen during the last print stroke by the squeegee. This
so-called kissing of the textile is accomplished by using as little
pressure on the screen as possible so as to have the textile barely
touching the screen when the squeegee passes thereover forcing the ink
therethrough. As a result, the last print stroke is at a very low
squeegee pressure.

[0008] In addition to the above, fibrillation is a common issue in screen
printing upon textiles. It generally means "fibers showing through." It
exists when fibers break through the layer of ink laid thereinover.
Specifically, instead of the ink totally covering the textile, sporadic
fibers will appear on the outermost surface of the ink. This will give
the product an unfinished or imperfect look. It will frequently affect
the appearance of the print for the color of the textile will appear in
the print giving the image a washed-out appearance. Fibrillation may also
cause poor resolution when the desired design relies on the textile
substrate for very small or fine parts of the design.

[0009] It has been found that abrasion of the area print upon can cause
the fibers of the textile to break loose from the surface of the ink,
giving the print a `washed-out` appearance.

[0010] Fibrillation is dependant on many variables, such as the ink weight
and viscosity, type of ink, type of textile and the weave of a textile.
For example, it is believed that the higher the ink weight the lesser the
chance of fibrillation. In addition, the tighter the fibers on the
surface of the textile the lesser the chance of fibrillation. Other
factors affecting fibrillation include the design of the print, the gaps
in the screen and thickness of the screen, viscosity of the ink, and the
cure times, also are factors.

[0011] One solution is to print the textile, flash it and overprint it
with a clear plastisol or water-based clear ink. This has been found to
minimize fibrillation. However, this can cause a glossing or mottling
effect.

[0012] Applicants of the present invention have observed that one cause of
fibrillation is the pressure applied by the squeegee during the print
stroke. Specifically, when the print stroke is completed, the screen
rebounds from the textile. At the same time, both ink and fibers are
drawn away from the textile. The result is that at times, fibers can be
drawn further from the textile than the ink causing fibers to overlay or
rest on top of the outer layer of ink.

[0013] Applicants have found that reducing the pressure to the squeegee on
the last stroke draws fewer fibers and covers the fibers drawn by prior
print strokes. Accordingly, a last kissing stroke can rectify
fibrillation or minimize it.

[0014] The present invention is provided to solve the problems discussed
above and other problems, and to provide advantages and aspects not
provided by prior automated printing machines of this type. A full
discussion of the features and advantages of the present invention is
deferred to the following detailed description, which proceeds with
reference to the accompanying drawings.

SUMMARY OF THE INVENTION

[0015] An aspect of the present invention is directed to an automated
screen printing apparatus comprising a multi-stroke printing head and a
means for controlling a source of pressure. The multi-stroke printing
head has a squeegee operatively engaged with the source of pressure. The
source of pressure transfers a force to the squeegee during printing. The
means for controlling the source of pressure selectively varies a force
applied to the squeegee from a first applied force applied during a first
stroke to a second applied force applied during a subsequent stroke.

[0016] The first aspect of the invention described above may include one
or more of the following features, alone or in any combination. For
example, the first applied force may not be equal to the second applied
force. The means for controlling the source of pressure may selectively
vary the force applied to the squeegee from the first applied force
applied during the first stroke to a plurality of applied forces applied
during a plurality of corresponding subsequent strokes. A digital voltage
regulator may provide the means for controlling the source of pressure.
An analog signal may provide the means for controlling the source of
pressure. The apparatus may further comprise a pressure gauge adjacent
the multi-stroke printing head, a control panel for selectively
controlling the means for controlling the source of pressure, and/or a
pressure display on the control panel. The means for controlling the
source of pressure may be adjustable via a display panel spaced from the
printing head. The means for controlling the source of pressure may be
adjustable at the multi-stroke printing head. Thus, the means for
controlling the source of pressure may be adjustable at a plurality of
locations positioned about the apparatus, including a remote location.
The means for controlling the source of pressure may be disabled wherein
the first applied force applied during a first stroke and the second
applied force applied during a subsequent stroke are equal in magnitude.
At least one piston may be provided to transfer the first and second
forces to the squeegee.

[0017] Another aspect of the present invention is directed to a printing
head for an automated screen printing machine. The printing head
comprises a squeegee operatively engaged by a source of pressure and a
means for varying a force applied by the source of pressure to the
squeegee.

[0018] This aspect of the invention may include one or more of the
following features, alone or in combination. The means for varying the
force applied by the source of pressure to the squeegee may selectively
vary the force applied to the squeegee from a first applied force applied
during a first stroke to a second applied force applied during a
subsequent stroke. The first applied force may not be equal to the second
applied force. The print head may further comprise a flood bar adjacent
the squeegee operatively engaged by a source of pressure.

[0019] Another aspect of the present invention is directed to a method of
screen printing a fabric target using an automated screen printing
apparatus comprising at least one printing head having a flood bar for
delivering a quantity of fluid to a screen and a squeegee for applying a
force by which at least a portion of the fluid passes through the screen
to the fabric target. The method comprises the steps of: (1) providing a
first relative movement between the squeegee and the screen; (2)
providing engagement between the squeegee and the screen with a first
force between the squeegee and the screen during the first providing
relative movement step; (3) providing a second relative movement between
the squeegee and the screen; and (4) providing engagement between the
squeegee and the screen with a second force between the squeegee and the
screen during the second providing relative movement step wherein the
first force is not equal to the second force. The screen may be laden
with a printing fluid.

[0020] Another aspect of the present invention is directed to a
turret-style printing apparatus. The apparatus comprises a plurality of
radial arms, a target area, a means for providing relative movement
between the target area and the printing head, a means for providing a
pressure between the squeegee and the target area, and a means for
regulating a pressure between the squeegee and the target area. The
plurality of radial arms each have a printing head associated therewith.
The target area is in alignment with at least one printing head wherein a
design is applied to a target article at the target area by the printing
head. The means for providing relative movement between the target area
and the printing head provides relative movement for multiple passes
between a squeegee and the target area. The means for regulating the
pressure between the squeegee and the target area regulates such that a
first pressure between the squeegee and the target area on a first stroke
is not equal to a second pressure between the squeegee and the target
area on a subsequent second stroke.

[0021] Another aspect of the present invention is directed to a method of
screen printing a fabric target. The method comprises the steps of: (1)
providing a printing head including screen having a pattern thereon, a
flood bar for delivering a quantity of an ink to the screen and a
squeegee for applying a force by which at least a portion of the ink
passes through the screen to the fabric target; (2) providing an
electro-mechanical means for providing movement to the flood bar and the
squeegee across the screen; (3) providing a source of pressure for
applying a force to the squeegee against the screen; and (4) providing a
means for regulating the source of pressure wherein the force applied to
the squeegee may be automatically varied from a first magnitude of force
applied on a first stroke of the squeegee across the screen to a second
magnitude of force applied on a second stroke of the squeegee across the
screen wherein the second magnitude of force is less than the first
magnitude of force.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To understand the present invention, it will now be described by
way of example, with reference to the accompanying drawings in which:

[0023]FIG. 1 view of a turret screen printing apparatus of the present
invention;

[0024]FIG. 2 is a perspective view of a print head in a first position;

[0025]FIG. 3 is a perspective view of a print head in a second position;

[0026]FIG. 4 is a block diagram of an aspect of the present invention;
and

[0028] While this invention is susceptible of embodiments in many
different forms, there is shown in the drawings and will herein be
described in detail preferred embodiments of the invention with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not intended to
limit the broad aspect of the invention to the embodiments illustrated.

[0029] Referring to FIG. 1, a typical turret style automated multi-stroke
printing press 10 is shown, including a central turret or base section 11
supporting a plurality of spaced apart, spoking, radial upper arms 30 and
radial lower arms 70. In the embodiment shown, the distal ends of the
lower arms 70 support metal pallets, flat beds, or platens 71 for
carrying a target article, e.g., a textile, a rug, or other substrate
(not shown), to be printed upon. The distal ends of the upper arms 30
support printing heads 31 or conventional, well-known curing units (not
shown), such that a curing station or printing head 31 is associated with
each arm 30. While the machine of the present invention is shown and
described having upper arms supporting printing heads or curing units and
the lower arms supporting pallets, it is, of course possible for the
upper arms to support the pallets and the lower arms to support the
printing heads or curing units.

[0030] One of the sets of arms 30,70 rotates around the base section 11.
In the embodiment shown, the lower arms 70 rotate relative to the upper
arms 30. This base section 11 includes, among other things, the unit's 10
supporting feet 12 and control panel 13.

[0031] The typical printing head includes a flood bar 33, a squeegee 34,
and a screen 35 (shown on a single printing head 31) supported by opposed
arms 32. Relative movement between the flood bar 33 and a target area,
which may include the screen 35, a target article, and the pallet 71,
causes the flood bar 33 to bring paint or ink to the screen 35. Upon a
relative movement by the squeegee 34 and the target area, the ink is
applied across the screen 35 by the adjacent squeegee 34. Together, a
print is formed on the textile.

[0032] These printing heads, or curing units, form stations. Ten (10) such
stations are shown in FIG. 1. The pallet 71 with the textile thereon is
rotated, indexed and registered at each station where the textile is
worked on, that being either printed upon or cured. Each arm 70 and
pallet 71 rotates through the ten stations. While it is appreciated the
upper arms can rotate relative to the lower arms or the pallets and
printing heads can be reversed, the present invention will be discussed
with the stationary printing heads attached to the upper arms and the
rotating pallets attached to the lower arms.

[0033] As illustrated in FIGS. 2 and 3 and as described above, the flood
bar 33 draws ink or paint across or to the screen 35. The squeegee 34
forces the ink or paint through openings in the screen 35 by applying
pressure as it is wiped across the screen. Each such pass by the flood
bar 33 and the squeegee 34, designated by arrows, is called a stroke. One
or more strokes may be carried out at each station. On each stroke, the
flood bar 33 is lowered under pressure supplied by a set of flood bar
pistons 72. The relative movements by the flood bar 33 and the squeegee
relative to the target area, are lateral movements or along a length of
the arms 30 controlled by servo motors (not shown). This means for
providing lateral movement or strokes may be performed by any number of
electro-mechanical devices including pulleys, screws, levers, hinges,
cams, etc. without departing from the spirit of the invention.

[0034] On a return pass, the flood bar pistons 72 remove pressure from the
flood bar 33 such that the flood bar 33 is raised. At the same time, a
set of squeegee pistons 76 provide a downward force (F) on the squeegee
34 while the electro-mechanical servo motors control the lateral return
pass, with pressure on the screen 35 supplied by the squeegee 34, to
complete the stroke. Broadly stated, engagement between the squeegee 34
and the fluid-laden screen 35 is accomplished by a first force (F)
between the squeegee 34 and the screen 35 during the relative movement
between the screen 35 and the squeegee 34. Preferably, the squeegee 34 is
operatively engaged with a source of pressure, in the preferred
embodiment a piston assembly, the source of pressure transfers the force
(F) to the squeegee 34 to bring the squeegee 34 into engagement with the
ink wherein the ink passes through the pattern on the screen to a target
article at a target location or area in alignment with the screen 35,
preferably a textile supported beneath a screen 35 on a pallet 71. This
engagement step is performed during a pass by the squeegee 34 over the
laden screen 35.

[0035] It is not necessary for the downward force (F) acting on the
squeegee 34 to be provided by a piston. Several other means for applying
the pressure can be provided without departing from the spirit of the
invention. For example, mechanical means may be employed, such as gears,
cams, screws, levers, servo-motors, and the like without departing from
the spirit of the invention.

[0036] Each piston 72,76 has a fluid pressure line 82 (gas or hydraulic)
in communication with a chamber 72a,76a. The piston rods 72b,76b transfer
a pressure to the flood bars 33 and the squeegees 34, respectively. The
transfer pressure is selectively variable via a control means associated
with the control panel 13. Accordingly, through a first stroke the
transfer pressure may be a first pressure value while the transfer
pressure may be a second pressure value, higher or lower, on the second
stroke. The second stroke may provide the kiss-level force (F) described
earlier. Stated another way, each station has a printing head which is
capable of a plurality of strokes to supply patterned ink or paint to a
target article to be printed upon with a design, typically a textile or
rug. Each subsequent stroke may be provided at a different squeegee
pressure than a stroke before it.

[0037] A further controlling means of the automated screen printing
apparatus 10 of the present invention further includes a means for
controlling the number of strokes at each station while the source of
pressure is also controlled or regulated. Thus, from a control panel 13,
a user may selectively the number of strokes while varying or regulating
the force (F) applied to the squeegee 34 from a first magnitude of an
applied force (F) applied during a first stroke to a second magnitude of
an applied force (F), e.g., greater than, less than, or equal to the
first applied force (F), during a subsequent stroke. Thus, the control
panel 13 includes a means for programming, controlling, or regulating 81
the magnitude of force (F) delivered by the squeegee 34 across the screen
35. (See FIG. 4). These forces may be varied over multiple strokes to as
many as nine or more pressure/force (F) variations on nine or more
strokes.

[0038] Typically, control of the apparatus functions is accomplished at
the control panel 13. However, these functions may also be carried out at
a small terminal controller 84 at each printing head 31 or remotely via
personal computing device, PDA, etc 86 and monitored on any number of
gauges 80 located on the control panel 13, near or adjacent the printing
heads 31, and or at the remote cite.

[0039] It is contemplated that the variable pressure may be controlled by
digital means (such as a digital voltage regulator, frequency, PWM,
communication networks (Modbus, CAN etc.)) or by analog means, such as an
analog signal in Hz (voltage 0-5V, 0-10V; current 0-20 mA, 4-20 mA). The
applicants further contemplate means for disabling this function any of
the control panels wherein the magnitudes of the forces applied by the
squeegee 34 are generally equal in magnitude.

[0040] This apparatus 10 may be used to perform a method 20. The method of
screen 35 printing a fabric target generally includes the step of
providing a first relative movement between the squeegee 33 and the
fluid-laden screen 35, preferably a stroke by the squeegee 34 over the
ink or paint-laden screen 35. Next, an engagement between the squeegee 34
and the fluid-laden screen 35 is provided with a first force (F) between
the squeegee 34 and the screen 35. This is performed during the first
providing relative movement step. A second relative movement between the
squeegee 34 and the fluid-laden screen 35 is carried out. At the same
time, engagement between the squeegee 34 and the fluid-laden screen 35 is
provided with a second force (F) between the squeegee 34 and the screen
35 wherein the first force (F) is not equal to the second force (F).

[0041] One specific example or method 200 of the present invention is
shown on the flowchart of FIG. 5. This method utilizes the apparatus 10
and functionality described above to accomplish the following steps:
(204) provide a silk screen apparatus, preferably a turret-style screen
printing apparatus having a plurality of print heads, each having a flood
bar and a squeegee electo-mechanically controlled to traverse back and
forth over a patterned screen; (208) load ink or other printing fluid
onto the patterned screen; (212) use the controller 13, the small
terminal controller 84, and/or the external controller 86 to select the
number of lateral strokes by the squeegee/flood bar combination across
the ink or printing fluid laden screen; (216) use the controller 13, the
small terminal controller, and/or the external controller 86 with the
force controller/regulator 81 to select the magnitude of force (F)
delivered by the squeegee 34 across the screen 35 on each pass; (220)
repeat steps (212)-(216) for each print head; (224) bring squeegee 34
into engagement with the printing fluid laden screen; (228) pass squeegee
over ink or printing fluid laden screen 35 to impart printing on the
target article; (232) repeat step (228) at desired magnitude of force (F)
applied to the squeegee 34 by automatically varying the force (F) applied
by the squeegee 34 via signal generated by the controller 13, the small
terminal controller 84, and/or the external controller 86; (236)
optionally, repeat step (228) wherein a force (F) applied to the target
article is a kiss-level force (F) to remove or highly reduce any
fibrillation; and (240)

[0042] While the specific embodiments have been illustrated and described,
numerous modifications come to mind without significantly departing from
the spirit of the invention, and the scope of protection is only limited
by the scope of the accompanying Claims.